Method for measuring the yaw velocity of a vehicle

ABSTRACT

Method of measuring the yaw velocity of a vehicle. An estimate of the yaw velocity is made by either a gyrometer or a steering angle sensor. This estimate is selectively readjusted when a fixed obstacle is sensed using periodic updates of the longitudinal speed of the vehicle, the distance from the fixed obstacle and the relative transverse speed of the obstacle.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns measurement of the loop speed of a vehicle,notably with a view to predicting its path.

2. Discussion of the Background

The loop speed of a vehicle can be estimated most simply by means of agyrometer or from its longitudinal speed and its steering angle.

Through patent FR 2,702,570, in the applicant's name, one learns of aprocess of detection and selection of obstacles presenting the risk ofcollision with a vehicle, called following vehicle. The processdescribed in that patent uses a horizontal scanning telemeter fordetermining the radius of curvature and angular speed of the followingvehicle, as well as an odometer for measuring its longitudinal speed. Onthe basis of those measurements, the system used estimates the danger ofa collision between the following vehicle and a selected obstacle, bycomparing their respective paths.

The measurement of angular speed made according to patent FR 2,702,570from measurements taken with a horizontal scanning telemeter is precise.However, it is not permanent, since it assumes that an obstacle has beendetected and selected. Furthermore, that measurement is marred byinaccuracies, linked to the presence of other selectable obstacles inthe field of the telemeter.

This invention is aimed at permanently obtaining a measurement of theangular speed of a vehicle as precise as possible.

SUMMARY OF THE INVENTION

It concerns a process of measurement of the loop speed of a vehicle.That process is characterized in that the course of said speedpermanently measured by an installed instrument is selectivelyreadjusted by means of indications corresponding respectively to thelongitudinal speed of the vehicle, to its longitudinal distance from afixed obstacle present on its path and to the relative transverse speedof the same fixed obstacle in relation to the vehicle.

According to one preferred embodiment of the invention, Dl and Vt areindicated by a horizontal scanning telemeter, in case of detection of afixed obstacle on the path of the vehicle.

In accordance with the invention, the loop speed of the vehicle can beestimated by a steering wheel sensor.

The invention also proposes that this estimate be made directly by meansof an installed gyrometer indicating the instantaneous loop speed of thevehicle.

To carry out readjustment of the angular speed, it is provided inparticular that the measurement of Dl, Vl and Vt by the telemeter shouldbe used to deduce the path curve χ of the vehicle.

In that case, the value of the curve χ so determined can be usedadvantageously to readjust the value of the deviation from origin b ofthe steering angle.

Other characteristics and advantages of the invention will be clearlyapparent on reading of the following description of one particularembodiment of the invention, in connection with the attached drawings,on which:

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 schematically represents a motor vehicle equipped with detectionand measuring instruments making it possible to use the invention, and

FIG. 2 specifies the nature of the measurements taking place in its use.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 indicates the presence on the vehicle 1 of an obstacle detectionapparatus 2, such as an infrared laser telemeter of L.I.D.A.R. (LightDetecting and Ranging) type placed in the center part of the front unit3. Of course, the center L.I.D.A.R. is not exclusively used, and one canjust as well envisage using other types of obstacle detectors orintegrating the detector in one of the two optical units 4 of thevehicle, without departing from the scope of the invention. A computer 5receives the return information from the telemeter 2, notably when thelatter has detected an obstacle on the path of the vehicle, as well asthe signals emitted by a longitudinal speed sensor of the vehicle 6,such as a wheel sensor of the A.B.S. system (Anti-Blokieuring-System) orany other speed sensor of the vehicle, by a steering angle sensor 7 orby a gyrometer 8 indicating the loop speed of the vehicle. Thatinstallation, supplemented possibly by a high head display 9 throughwhich the driver 11 can have a visual warning signal in his usual fieldof vision, makes it possible in known fashion to detect the obstaclespresent on the path of the vehicle, to select certain particularlyhazardous obstacles among the latter by comparing their relativelongitudinal speed (cf. FIG. 2) with the longitudinal speed Vl of thevehicle, and to secure remote control of the vehicle in relation tocertain selected obstacles, such as vehicles traveling on the sametraffic lane, by acting directly on the control unit of the throttlevalve 12 and/or on the control housing of the automatic transmission 13and on the brake acceleration pedals 14, 16.

FIG. 2 reveals the indicators taken into consideration to define thepath of a vehicle 1 in relation to an obstacle 17 detected in the fieldof observation of a telemeter. The vehicle moves at a longitudinal speedVl estimated by the above-mentioned speed sensor 6 and vectoriallyoriented in the direction of the obstacle 17, in the event that theobstacle in question is sufficiently distant from the vehicle.Furthermore it possesses a loop speed Ψ linked to the curvature of itspath χ and to the longitudinal speed Vl by the relation ##EQU1##

Finally, the telemeter 2 is capable of measuring the longitudinaldistance Dl of any detected obstacle and of measuring the relativelongitudinal speed Vr and the relative transverse speed Vt of thedetected obstacle 17 in relation to the vehicle 1. By comparing thelongitudinal speed Vl of the vehicle 1 measured by the sensor 6 and therelative longitudinal speed Vr of the obstacles, the above-mentionedcomputer 5 is then capable of selecting the fixed obstacles, since forthe latter Vr=Vl.

Furthermore, it is known that for these fixed obstacles, the loop speedΨ of the vehicle is precisely linked to their passing speed ortransverse speed Vt by the relation ##EQU2##

The loop speed Ψ of the vehicle can then be determined by the telemeterwith precision every time a fixed obstacle is detected, thanks to theapplication in the computer 5 of that relation to the values Dl and Vtmeasured by the latter.

In addition, considering that the loop speed Ψ of the vehicle is linkedto the curvature of its path χ by the relation ##EQU3## it is thenpossible to determine the exact value of the curvature, that is,##EQU4##

When the vehicle 1, furthermore is equipped with a steering angle sensor7 or a gyrometer 8, either of those apparatuses makes it possible toestimate in real time the loop speed of the vehicle. In practice, suchestimates prove too imprecise to be applied without correction tocalculation of the path of the vehicle and to the prediction ofcollisions with obstacles occurring in that path. This invention istherefore intended to take advantage of the measurements made by thetelemeter on the detection of fixed obstacles in order to readjust theestimate of loop speed supplied by a gyrometer or a steering anglesensor.

In the case of a gyrometer directly supplying an estimate of the loopspeed of the vehicle, the desired correction can be made by readjustingthe estimates to the exact measurements established by means of atelemeter, on the detection of a fixed obstacle.

If, on the other hand, the vehicle 1 is equipped with a steering anglesensor, it is known that the steering angle measured δ is linked to thecurvature χ by the kindred relation δ=aχ+b, in which a depends on thegear reduction and wheelbase of the vehicle and b is a deviation fromorigin, a function of the error introduced by the sensor 7 itself and bytransverse forces (wind, centrifugal force, takes) undergone by thevehicle.

According to the invention, the curvature of the path χ is estimatedfrom the measurement δ of the sensor 7 in the absence of a fixedobstacle and these measurements are readjusted by recalculating thedeviation from origin b on the basis of the curvature determined by thetelemeter when the fixed obstacle is detected. Between the detection oftwo fixed obstacles, the measurement of curvature χ from the steeringangle δ thus benefits from the correction introduced in the deviationfrom origin b thanks to the last precise punctual measurement of thelatter, obtained by means of the telemeter.

In order to make the readjustments of deviation of steering angle b, theinvention proposes, notably using the methods of calculation known asleast squares methods, but it is also possible to envisage theapplication of other algorithms requiring, according to a preestablishedperiodicity or solely as a function of the obstacles detected, acorrection or "hybridation" of the value of the curve determined by thesteering angle sensor, or of the value of the angular speed estimated bythe gyrometer, by means of values calculated by the telemeter.

In conclusion, the invention makes it possible to obtain permanently ameasurement of the loop value of a vehicle, sufficiently reliable tomake it possible to predict the risks of collision of the vehicle withall of the obstacles presenting a risk of collision. This reliability isbased on the precision of measurements made by the telemeter on thefixed obstacles encountered and the corrections introduced as often aspossible in the usual measurements of the curve or of the loop speed ofthe vehicle.

I claim:
 1. A process for measuring a loop speed of a vehicle,comprising the steps of:providing a loop speed measuring device whichprovides an estimate of said loop speed; adjusting said loop speedmeasurement device when a fixed obstacle is detected in a path of thevehicle, said adjusting being related to a longitudinal speed of thevehicle, a longitudinal distance from the vehicle to the fixed obstacleand a relative transverse speed of the fixed obstacle in relation to thevehicle.
 2. The process for measuring according to claim 1, wherein thelongitudinal speed, longitudinal distance and relative transverse speedare detected by a horizontal scanning telemeter.
 3. The process formeasuring according to claim 1, wherein said loop speed measuring deviceis a steering angle sensor.
 4. The process for measuring according toclaim 1, wherein said loop speed measuring device is a gyrometer.
 5. Theprocess for measuring according to claim 1, wherein said longitudinalspeed, said longitudinal distance and said relative transverse speed areused to determine a path curve of the vehicle.
 6. A process formeasuring according to claim 5, wherein the path curve is determined soas to adjust the value of deviation of the steering angle according tothe equation δ=aχ+b, where δ is a steering angle, χ is the path curve, ais the coefficient of gear reduction of the vehicle and b is thedeviation of the steering angle.
 7. A process for measuring according toclaim 6, wherein the adjusting of the deviation of the steering angleuses a least squares method.